An Observational Analysis of Ocean Surface Waves in Tropical Cyclones in the Western North Pacific Ocean

Knowledge of ocean surface waves in tropical cyclones (TCs) is necessary to calculate air-sea exchanges of momentum and enthalpy for improved TC predictions. Here we use 24 years (1992-2015) of TC and significant wave height (SWH) observations in the western North Pacific to analyze storm-following waves within the TC. The SWH was composited according to the TC translation speed, U-h, and TC intensity based on V-m, the maximum 10-m wind speed. The results show that SWH is largely symmetrical for slow-moving TCs when U-h is less than 3 m/s and is asymmetric for faster-moving storms with larger waves in the right-front quadrant referenced to the TC heading. For a class of TCs translating at a medium U-h between 3 and 7 m/s, a little less than the waves' group speed, near resonance leads to strong asymmetry with over 50% of waves with SWH exceeding 7-8 m on the right-front quadrant. As V-m intensifies to 50 m/s and greater, extreme waves develop and become saturated: SWH approximate to 10-11 m, corresponding to when, as shown in previous studies, the momentum exchange coefficient C-D levels off while the enthalpy exchange coefficient C-k may increase. Over 80% of the saturated waves then reside in the right-front quadrant, indicating the quadrant's dominant influence on C-D and C-k. The medium-translating TCs were found to have a greater propensity for intensification than other types of TCs. Our results suggest a link between TC intensity, translation, and wave saturation and asymmetry in the right-front quadrant.